System for testing sequential code selector



July 25,1961

J. T. NEISWINTER SYSTEM FOR rlESTING SEQUENTIAL CODE SELECTOR 5sheets-snee@ 1 original Filed Jan. 2 0. 1955 WSI MOIQHMB 9, IU SMV.mmdklbl UNI.

l New w .um

A TTORNEY July 25, 1961 .1. T. NElswlNTER SYSTEM FOR TESTING SEQUENTIALCODE SELECTOR July 25, 1961 1. T. NElswlNTl-:R

SYSTEM FOR TESTING SEQUENTIAL CODE SELECTOR 5 Sheets-Sheet 3 OriginalFiled Jan. 2,0. 1955 /NVENTOR J. 7i NE'ISW/NTER m. Gt

las

5 Sheets-Sheet 4 www@ J. 7T NE/SW/NTER J T. NEISWINTER 1c. v ./Nmv will.

n.25 TQQ SYSTEM FOR TESTING SEQUENTIAL CODE SELECTOR (mvv v July 25,1961 original Filed Jam.l 20. 1955 A TTORNEV July, 25, 1961 1. r.NEl'swlNTER SYSTEM FOR TESTING SEQUENTTAL coDE SELECTOR l5 sheets-sheet5 Original Filed Jan. 20. 1955 Jar/.Ls anims/vwl By frhacw m. .um

A TOR/VEY 8 Claims. (Cl. 178-4.1)

This application is a division of my application Serial No. 482,983, ledJanuary 20, 1955, which issued as Patent No. 2,952,733 on September 13,1960.

This invention relates to communication systems and particularly totelegraph communication systems including switching equipment forautomatically directing and tranmitting messages from a station oforigin to a station of destination through one or more switching centersin accordance with and under the control of directing or addresscharacter signals preceding the message and endof-message signalsfollowing the message.

An automatic teletypewriter switching system of the type wherein thepresent invention may be adapted for use is found, for example, inPatent 2,766,318, issued October 9, 1956, to W. M. Bacon, G. I. Knandel,I. A. Krecek and G. A. Locke. The system comprises a telegraph centraloffice, or switching center, and a plurality of line circuitsrespectively extending therefrom to a plurality of outlying mainstations. In the Bacon et al. patent, supra, it becomes desirable topermit transmission from any of the outlyingstations to the telegraphcentral oflice. Such transmission is automatically controlled from thecentral ofce by sending periodically therefrom groups of code signalsidentified as transmitter start patterns, the functions of which are tostart transmission from the outlying stations in any predeterminedsequence. The transmitters at the outlying stations are selected intheir turn by single code combinations whereas the receivers, such asprinters and reperforators, at such stations are selectively connectedto the line circuits for receiving messages from the central office byaddress codes comprising a sequence of two code combinations. Theseaddress or directing codes are referred to herein as receiver cut-oncodes.

To accomplish selection of a desired station, a selector equipped withmeans capable of responding to a transmitter start pattern and areceiver cut-on pattern is provided at outlying stations. This type ofselector is identified as a Sequentially Operated TeletypewriterUniversal Selector, or what is generally known as a SOTUS unit shown anddescribed in the Bacon et al. patent, supra. It is provided withcontacts that are respectively responsive to the single and two codesignal combinations for performing the necessary switching of thetransmitter and receiver into operative connection with its respectiveline circuit. A SOTUS unit is located at each outlying station and isalways connected to the line circuit, and monitors all trac passing oversuch circuit. The disclosure of the Bacon et al. patent, supra, istherefore incorporated herein, by reference, as part of the presentspecification.

An object of the invention is to automatically produce at a telegraphcentral oice and to automatically transmit over any one of a pluralityof line circuits extending from the central oice to the respectivestation a distinctive series of test signals for checking the operationof the SOTUS unit at such station in response to a single request of amaintenance man thereat made at the start of operations.

States arent ,O

ice

Another object is to eliminate the services of an attendant at thetestboard in the telegraph central oice during the time that themaintenance man at an outlying station is checking the SOTUS unit atsuch station.

Heretofore, the source of teletypewriter test signals used for testingmachines at outlying stations has been separate strips of perforatedteletypewriter tape for each machine and for each type of test signalsrequired for such machine. This tape method has been unsatisfactory dueto the work required to prepare the tape with the necessary signal codeperforations and the diiculties in storing and maintaining a largenumber of such prepared tapes in a test room. Another objection to theuse of a tape is that the services of a testboard attendant tosubstitute tapes is required very frequently by the maintenance manduring the testing operations.

A feature of the invention is the provision at a central oflice of meansresiding in a coordinate array of connecting points having a pluralityof abscissas and a plurality of ordinates whereby each abscissa iscapable of producing a plurality of distinctive permutation code signalsarranged to be automatically selected and transmitted to any one of aplurality of outlying stations, as desired, in response to a requestfrom such one of the outlying stations.

Another feature is the provision of means at a central oice responsiveto one or more break signals received from any one of a plurality ofoutlying stations for selecting certain desired groups of thepermutation code signals and for automatically transmitting each signalof such certain groups, in turn, to that one of the outlying stations.For example, in response to one break signal, the transmitter startpattern of permutation code signals for such one station is selected andautomatically transmitted; in response to two break signals, thereceiver, or printer, cut-on pattern is selected and automaticallytransmitted; in response of four break signals, permutation code signalsfor letters R and Y are lautomatically transmitted alternately, each ofthe R and Y signals having switched bias; and in response to live breaksignals or one break signal following the four break signals which weretransmitted for the R and Y switched bias signals, permutation codesignals for letters R and Y are automatically transmitted alternately,each of the R and Y signals having switched end distortion.

Still another feature is the provision of means at a central officeresponsive to three break signals from any one of a plurality ofoutlying stations for operating a signal at a testboard at the centraloice indicating to the testboard attendant that a telephonie connectionis desired between the testboard and that outlying station.

Another feature isthe provision of ymeans at a central office, includingan electronic timing circuit for restoring the break signal responsivemeans to its normal position should no additional break signals bereceived within an interval of predetermined duration. With thisprovision the maintenance man at an outlying station knows Iat all timeswhat kind of test signals he has elected to receive fro-m the centraloflice inasmuch as the selector switch brushes are returned to normal inresponse' to one or more break signals transmitted from the outlyingstation during the time that test signals are being transmitted to theoutlying station in response to a previous request.

Another feature -is the provision of means at a central oice, responsiveto one or more incoming break signals and having a plurality ofrotatably stepping members arranged to simultaneously operate throughone step for each permutation code signal automatically transmitted toan outlying station, the stepping operation being successively performedthrough an angular distance of almost 360 degrees and then repeateduntil another break is received.

The present system includes means at a central oce, having a singlerotatably stepping member arranged to operate through one step each timethat the means having the plurality of rotatably stepping membersoperate through an angular distance of almost 360 degrees, whereby'different groups of permutation code signals are selected for automatictransmission to an outlying station.

The present system includes also means operative in response to the stoppulse of each of the permutation code signals automatically transmittedto the outlying station when the selecting means responsive to the breaksignals has been conditioned in response to the four or tive breaksignals for automatically transmitting the permutation code signals forthe letters R and Y alternately to an outlying station.

The foregoing objects and features of this invention may be more readilyunderstood by the following description when read vin reference to thedrawings of which:

FIG. l shows the relative arrangement of FIGS. 2 to 6;

FIGS. 2 to 5 and the left-hand portion of FIG. 6 show the equipment atthe telegraph central oice or switching center, and` the right-handportion of FIG. 6 shows in block Lform two main stations whereat theSOTUS unit at each is adapted for connection to the telegraph centraloffice for receiving the test signals produced thereat;

FIG. 2 shows in the extreme left-hand portion thetransmitter-distributor circuit used for sending to the line circuitteletypewriter test signals;

FIG. 2 in the remaining portion and FIG. 3 show the selector controlcircuit responsive to the break signals incoming over a line circuit ofan outlying station for selecting the desired test signals automaticallyproduced at the telegraph central ofce, and for directing such desiredtest signals to the line circuit of Such outlying station;

FIGS. 4 and 5 show the teletypewriter character signal control circuitsfor automatically producing the desired test signals upon request fromthe maintenance man at any one of the outlying stations;

FIG. 6 shows (l) in the left-hand portion, in skeletal form, theequipment in the test room at the central telegraph oice, (2) in thelower portion, in block form, a telegraph central otice which forms apart of the regular telephone commercial system, and (3) in theright-hand portion, two outlying stations of a plurality whereat theSOTUS units are arranged to receive the desired test signals from theirrespective teletypewriter character signal control circuits.

It is to be understood Ithat the equipment shown in FIGS. 2 to 5,inclusive, represents an embodiment of the present invention.

The invention provides automatically operated and controlled means forpermitting a maintenance man at an outlying main station to test theSOTUS unit at such station with teletypewriter test signalsautomatically produced at the telegraph central oflce without the aid ofa testboard attendant other than to have such attendant establish theoriginal connection land effect the necessary disconnection when thetests are completed. The SOTUS unit may be of the type disclosed inPatent 2,502,654, granted April 4, 1950, Ito G. S. Keys, and Patent2,568,264, granted September 18, 1951, to W. I. Zenner.

GENERAL DESCRIPTION The use of reference characters on the drawingsfollows a definite plan. In FIGS. 2 to 5, inclusive, all apparatus shownhave reference character designations consisting of numerals andletters, the rst digit of each reference designation corresponding tothe number of the figure in which the apparatus so designatedis located.

All other parts of 'the system including both apparatus andinterconnecting conductors are designated with numerals whereof the rstor hundreds digit designates the ligure in which lthe particular part islocated.

The equipment provided at the telegraph central oflce comprises aplurality of teletypewriter character signal controlled circuits, onefor each outlying main station, wherein the teletypewriter test signalsare automatically produced; a selector control circuit automaticallyresponsive to request of a maintenance man at an outlying station forselecting any desired teletypewriter test signals to be produced by theparticular teletypewritcr character control circuit assigned to thatstation; a transmitterdistributor circuit for transmitting to theoutlying station the desired signals requested by the maintenance man;and a testboard whereat `an attendant in response to a telephonierequest from a maintenance man, may establish a connection between adesired teletypewriter character signal control circuit and the callingline circuit. The teletypewriter character signal control circuits areindividual to the line circuits terminating at the central office.

Teletypewrter character signal control circuit A teletypewritercharacter signal control circuit is provided for each of the outlyingstations of the system. Each of these circuits automatically produces asuccession of teletypewriter character signals without tbe use of aperforated teletypewriter tape. Each teletypewriter character signal isdetermined by the connection of a group of from one to ive small neonlamps to their respective code segments of a transmitter-distributor,one lamp being required for each spacing element in a teletypewritercharacter signal. This circuit is intended primarily for use inproducing the necessary teletypewriter character signals required totest a SOTUS unit at an outlying station in the system disclosed in theBacon et al. patent, supra.

The neon lamps used are provided in horizontal rows of lamp sockets, thelamp sockets being of the regular switchboard type. A bank of five rowsof sockets, each row containing forty sockets, provides for theproduction of forty teletypewriter character signals, each vertical rowof tive sockets in the bank being assigned for a teletypewritercharacter signal. The first or uppermost lamp socket of a vertical rowof live corresponds to the rst selecting element or pulse of a charactersignal, the second socket with selecting pulse No. 2, and so on. Theteletypewriter character signal is determined by inserting a neon lampin each socket associated with a selecting pulse that is to be a spacingelement of the signal. The absence of a lamp in a socket causes thecorresponding pulse to be a marking element.

Four forty-character signal lamp socket banks, as described above, areprovided for testing a SOTUS unit at each outlying station to be servedin the system disclosed in the Bacon et al. patent, supra. An attendantat the testboard in the telegraph central otlice, in response to atelephonie request from a maintenance man at an outlying station,operates a key whereby the bank of lamp sockets assigned to the callingstation is selected for connection to the line circuit to which theSOTUS unit at the calling station is connected, one key being providedfor the SOTUS unit at each of the outlying stations.

The rst or uppermost bank of lamp sockets of each group of four banks isused to provide a transmitter start pattern of signal combinations fortesting the SOTUS unit at a calling station while the lower three banksare used to provide the calling station teletypewriter printer orreceiver cut-on pattern. A sequence of forty-character signals is thusavailable for the transmitter start patterns and 1Z0-character signalsfor the receiver cut-on patterns.

The teletypewriter character signal control circuit also providesalternate R and Y signals, with either 20 D percent switched bias or 20percent switched end distortion.

Reference herein to the teietypewriter character signal control circuitsis had by designating the circuit shown in FIG. 4 as circuit 4CCC withits lamp socket banks designated, from top down, 4A', 4B', 4C and 4D',respectively, and that in FIG. as circuit SCCC with its lamp socketbanks accordingly designated 5A', 5B', SC' and 5D', respectively. Thelamp sockets themselves are designated with combinations of numerals andletters according to the banks in which they are located and theintersections at which the coordinate verticals and horizontalconductors may be respectively interconnected by means of the sockets toform energizing circuits for the neon lamps that may be inserted in suchsockets for transmitting a spacing pulse when desired as part of afiveunit code signal, the last character of each reference designationindicating the element of elements Nos. l to 5 of the code signal. Thevertical conductors are designated V1 to V40 representing theforty-character signals and extend through all the teletypewritercharacter signal control circuits 4CCC, SCCC, etc., of the system. Thehorizontal conductors are arranged in four groups of five each and aredesignated according to the banks wherein they form with the verticalconductors the points of intersection for the lamp sockets. Thehorizontal conductors for bank 4A are designated 4AH1 to 4AH5,respectively; for bank 4B', 4BH1 to 4BH5, respectively; and so on foreach of banks 4C and 4D. The horizontal conductors of banks 5A aredesignated 5AH1 to SAHS, respectively, for banks 5B', 5BH1 to SBHS,respectively; and so on for each of banks 5C and 5D. The lamps disposedin sockets at the conductor intersections in bank 4A are designated atvertical conductor V1 as 4A1-1 to 4A1-5, respectively; at verticalconductor V5, as 4A5-1 to 4A5-S, respectively; at vertical conductorV21, as 4A21-1 to 4A21-5, respectively. Those at the conductorintersections in bank 4B at Vertical conductor V1 are designated 4B1-1to 4B1-5, respectively; and those in bank 5A at vertical conductor V1are designated 5A1-1 to SAI-S, respectively, and so on.

Each bank of lamp sockets is selectively associated with thetransmitting apparatus by a relay, and four such relays for eachteletypewriter character signal control circuit are selectively preparedfor operation by operating a manually operable key, such as any one ofkeys 607, 608, etc., at the testboard, one key being provided for eachof the teletypewriter character signal control circuits 4CCC, SCCC, etc.The relays for banks 4A', 4B', 4C and 4D' are respectively designated4R1, 4R2, 4R3 and 4R4. Each group of bank relays, such as 4R1, 4R2, 4R3and 4R4, is controlled by a common relay, such as relay 4C for theteletypewriter character signal control circuit 4CCC shown in FIG. 4 andbank relays SR1, SR2, SRS and 5R4 of teletypewriter character signalcontrol circuit SCCC are controlled by common relay 5C. Relays 4C, 5C,etc., are controlled by the testboard keys 607, 608, etc., individual tothe signal control circuits 4CCC, SCCC, etc. The bank relays, such asrelays 4R1 to 4R4 and SR1 to 5R5 are selected for operation overcontacts of selector switches ZSWA and ZSWB which are responsive tobreak signals incoming over a line circuit from any one of the outlyingstations, as will be hereinafter described.

The plurality of signal control circuits 4CCC, SCCC, etc. are undercontrol of the selector control circuit which will be hereinafterdescribed to show how the maintenance man at an outlying station maycall, by means of break signals, independently of the services of atestboard attendant, for any test signals .that he may desire from thesignal control circuit assigned to his station, and in response to thosebreak signals the signal control circuit assigned to the calling stationimmediately transmits through a rotary distributor to the SOTUS unit atthe calling station the particular signals requested, such as any ofthose signals which constitute the following: The transmitter startpattern, the receiver cut-on pattern, the receiver disconnect pattern,the alternate R and Y signals with 20 percent switched bias or with 20percent switched end distortion. This is done by the maintenance mansending break signals over the line circuit, one break signal causingthe desired signal control circuit to` produce and send the transmitterstart pattern; two break signals, the receiver cut-on patterns; fourbreak signals, the receiver disconnect pattern (Figures and H) followedby the alternate R and Y signals with 20 percent switched bias and oneadditional break signal at this time changing 20 percent switched biasin the alternate R and Y signals to 2O percent switched end distortion.At any time that test signals are being transmitted to the line circuit,except when such signals are the alternate R and Y signals with Switchedbias, one break signal sent by the maintenance man will stoptransmission. The system requires that means be provided at the outlyingstation for the maintenance man to break on the line circuit fortelephonie communication with the testboard attendant and therefore atelephone handset is provided at the outlying station so that when thetestboard attendant is signaled he can connect his telephone headset tothe line circuit in order to talk with the maintenance man. To establishthis telephonie connection, the maintenance man sends three breaksignals to cause signal lamp 612 at the testboard to light and thenplugs the station handset 619 into jack 618 of the line circuit. Theattendant upon observing the lighted lamp, removes the right-hand plugof patching cord 61dl from jack 616 and 'substitutes plug 614 of hisheadset 615 whereby a telephonie connection is established betweenheadset 615 and handset 619.

The selector control circuit The selector control circuit which iscommon to all the signal control circuits 4CCC, SCCC, etc., ashereinbefore stated, comprises three rotary switches, the relaysnecessary to step the rotatable brushes of such switches in response tothe break signals received from the line circuit, the relays and thespace discharge tubes for producing the Figures, H, R and Y signals andfor creating the 20 percent switched bias and switched end distortion inthe R and Y signals. The rotary switches 2SWA and ZSWB are of theselector type and are responsive to the break signals transmitted fromthe outlying station for selecting the desired transmitter start and thereceiver cut-on patterns from those produced in the signal controlcircuits. Rotary switch ZSWC is of the stepping type and serves todirect the selected transmitter start and receiver cut-on patterns backover the line circuit to the SOTUS unit at an outlying station. SwitchZSWA has two banks of ten contacts each. Stepping switch ZSWC has tivebanks of twenty-two contacts each and selector switch ZSWB, which hasone bank only of ten contacts, is operable one step each time the brushon bank No. 3 of stepping switch ZSWC rotates to engage its contact No.22. The contacts of switches ZSWA and ZSWB serve to select for operationthe bank control relays 4R1 to 4RS, SR1 to 5R5, etc., and the contactsof banks Nos. l and 2 of switch ZSWC serve to close energizing circuitsextending through the lamps in the sockets in the forty verticalconductors which extend through all the signal control circuits 4CCC,SCCC, etc.

GENERAL THEORY OF OPERATION Creation of a single character signalTransmitter-distributor 2TD has a source of positive potential of volts,such as one o-f sources 401, 503, etc., in any of the signal controlcircuits 4CCC, SCCC, etc., connectable .to its inner ring in a circuittraceable over conductor 2.01, front contact and outermost upperarmature 4 of a relay controlling the Operation of the selected signalcontrol circuit, such as relay 4C of the circuit 4CCC. The start segmentof distributor ZTD is connected in a path extending over conductor 202,resistor 2R20, neon lamp 2N1, conductors 20S and 204, to the grid ofvaccum tube SBI. Vacuum tube SBI is normally nonconducting due to asource S01 of grounded negative potential of 130 volts being connecteddirectly to its grid through resistor 3R22 of high resistance value.When the distributor brush of distributor ZTD starts rotating over thestart segment at a time when relay 4C is in operated condition, assumingthat its respectively associated locking key 607 is operated at atelephonie request from the outlying station to which signal controlcircuit CCC is assigned, the positive source 401 of potential isconnected in a circuit extending over conductor 201 to the start segmentto cause neon lamp 2N1 to re and the positive voltage of 130 Voltsoverrides the negative voltage of 130 volts through the high resistanceof resistor 3R22, to make the vacuum tube SBI conducting. Vacuum tubeSBI is the rst of four tubes connected in cascade, the three othervacuum tubes being designated S132, SC1 and SC2. Vacuum tubes S132 andSC2 are normally conducting and vacuum tube SCI, like vacuum tube SBI,is normally non-conducting. Vacuum tube SC2, being normally conducting,normally supplies marking current through its cathode to the winding ofsend relay SSD. Relay SSD transmits all signals repeated by vacuum tubeSC2 to conductors S11 and S13 which are adapted for connection to any ofthe line circuits. Therefore, when vacuum tube SBI is made conducting bythe distributor brush passing over the start segment which always sendsa spacing pulse, the last tube, namely tube SC2, is made non-conducting,and reverse current in the path extending from grounded source S ofnegative potential of 130 volts, resistor 3R15 and the windings of relaySSD operates the relay to its spacing or right-hand contact therebytransmitting a spacing pulse to the connected line circuit. The fourtubes SBI, S132, SCI and SC2, being arranged in cascade, are used topermit adding switched bias or switched end distortion to the signals aswill be described hereinafter.

It the rst code or selecting pulse of the character signal transmittedfrom the selected signal control circuit is a spacing element, aconnection is made traceable from code segment No. l, over conductor 2P1included in dot and dash line 215 representing the ve conductors 211 toZPS, front contact and armature No. l of an operated relay, such asrelay 4111, assuming that key 607 at the testboard is in its operatedposition, and a neon lamp 4A1-1, vertical conductor V1 of the signalcontrol circuit u@CCC which is one of twenty conductors represented bydot and dash line 402, rotatable brush on the corresponding contact,such as contact No. l of bank No. 1 of switch 2SWC, conductors 205 and206, contact No. l or 2 and rotatable brush of the front bank ofselector switch 2SWA, conductor 207, resistor 2R21, conductor 204 to thegrid of vacuum tube SBI. Thus when the brush of distributor 2TD passesover segment No. 1, source 401 of positive potential of 130 volts willagain be connected to the grid of vacuum tube SB1, making tube SBIconducting and tube SC2 non-conducting, to operate relay SSD to itsright-hand or spacing contact.

For each of the following code pulses that is to be spacingj aconnection is made through the proper code segment of distributor ZTDand one of the neon lamps A1-2, 4A1-S, 4A1-4 and 4A15 to the grid ofvacuum tube SE1 so that when the rotatable brush passes over the segmentthe positive potential at source 401 will be momentarily impressed onthe grid of tube SE1. If a code pulse is to be marking no connection ismade from the particular code segment inasmuch as there is no neon lampin the socket at the corresponding intersection of the horizontal andvertical conductors, such as conductor 4AH-2 and vertical conductor V1.When the rotatable brush passes over a selecting code segmentcorresponding to a marking element of a character signal, there will beno source of positive potential connected to the grid of tube SBI andthe negative voltage of source S01 applied through resistor 3R22 of highresistance value to the grid of tube SBI will, therefore, cause the tubeto become non-conducting and consequently tube SC2 will becomeconducting to operate relay SSD to its left-hand or marking Contact.Relay SSD, upon operating to its marking contact, transmits a markingpulse to the line circuit.

For the stop pulse or element of the character signal, no connection ismade from the stop segment of distributor ZTD to the grid of vacuum tubeSBI and, accordingly, this pulse will always be a marking element.

With the arrangement just described, the continuous operation of thedistributor will cause the character signal established by theconnections of the neon lamps in the sockets of the signal controlcircuit 4CCC to be repeated continuously. To permit a sequence ofdierent character signals to be sent, relay 2P5 is operated through theconduction of vacuum tube 2D1 by the fifth code pulse transmitted in acircuit traceable from grounded source 401 of positive potential ofvolts, armature No. 4 and front contact of relay 4C, conductor 201,inner ring and segment No. 5 of the distributor ZTD, conductors ZPS and217, resistor 2R33 to the grid of vacuum tube 2D1. Vacuum tube 2D1, uponconducting, operates relay 2P5. Relay ZPS', upon operating, closes acircuit extending from grounded source 208 of negative potential of 24volts, through the winding of stepping magnet ZSTPC, conductor 209, backcontact and upper armature of relay SRY, back contact and upper armatureof relay SFI-I, conductor 214, to ground at the front contact andarmature of relay ZPS' and stepping magnet ZSTPC operates to stepselector switch ZSWC one step during the stop pulse of each charactersignal.

The grid of Vacuum tube SBI is connectable through the brushes of banksNos. 1 and 2 of rotary switch ZSWC to the vertical conductors Vil toV40. A diferent group or combination of from zero to five neon lamps maybe inserted in the tive sockets on each of vertical conductors V1 to V40for each bank of a selected one of the signal control circuits. Each ofthese combinations, in turn, is connectable through relay contacts tothe code segments of distributor 2TD. Thus the character signal for eachstep of the rotary switch ZSWC is determined according to which socketsof the tive of a group on a vertical conductor within a bank areoccupied by neon lamps. lAs hereinbefore stated, the start segment ofdistributor 2TD is always connected directly through a neon lamp 2N1 tothe grid of vacuum tube SBI and the stop segment has no connection tothe vacuum tube SBI. Therefore, the start pulse of the character signalwill always be a spacing element and the stop pulse will always be amarking element. If a contact in either of banks Nos. l and 2 of rotaryswitch ZSWC has no connection through any neon lamps in the signalcontrol circuit to the segments of distributor 2TD, all five code pulsesof the character will be marking" and the Letters signal will betransmitted to the line circuit. If a Contact in bank No. l or 2 isconnected through neon lamps to all tive code segments of distributorZTD, all tive selecting pulses will be spacing elements and the blanksignal will be transmitted to the line circuit.

Reason for using neon lamps When a large number of teletypewritercharacter signals are to be sent in sequence, necessitating using arotary selector switch having many contacts or a rotary selector switchwith several rows or banks of contacts arranged by means of relays forthe rows to be connected in sequence, a large number of alternateso-called sneak paths exists between the distributor segments and thecontacts of the rotary selector switch. lf resistors or even varistorswere used in place of neon lamps in the connections between thedistributor segments and the steps of the rotary selector switches, thecombined parallel resistance of so many paths would be so low as to makethe circuit unworkable.

With the use of neon lamps in these paths in the signal control circuit,the voltage across the direct path extending from, say, source 401 ofpositive potential of 130 volts, armature No. 4 and front contact ofrelay 4C, conductor 201, continuous ring and any one segment ofdistributor 2TD through the corresponding front contact and armature ofan R relay, such as relay 4R1, the neon lamp disposed in the socketconnected between that armature and one of the vertical conductors V1 toV40 included in dot Iand dash line 402, contact on either of banks Nos.l or 2 of stepping switch 2SWC, conductor 206, Contact and brush of thefront bank of selector switch 2SWA, conductor 207, resistor 2RM,conductor 204, the grid and cathode of tube 3Bl, to source 303 ofnegative potential of 24 volts wherein a total of 154 Volts is had. Avoltage of 90 volts is suflicient to cause the neon lamp in the directpath to lire. Each of the alternate paths involves three neon lamps intandem, however, and the total voltage used in the system is insulcientto lire this number of lamps in tandem. The result is that all alternateparallel paths are completely open and thus an unlimited number ofteletypewriter character signals can be produced with no effect whateverdue to parallel path currents.

Remote control by means of "break signals The various types ofteletypewriter character signals produced by a signal control circuitcan be selected in response to break signals received from the linecircuit. The teletypewriter character test signals are transmitted, inreturn, to the outlying station from which the break signals werereceived. These break signals normally will be transmitted by amaintenance man at the outlying station. -Each break signal transmittedover the line circuit operates selector switch 2SAW in a circuittraceable from ground at the lower armature and back contact of normallyoperated relay SLS (assumed to be released by the break signal), innerlower Iarmature and back contact of relay 3ST, conductor 304, throughthe winding of stepping magnet 2ST PA, conductor 210, front contact andarmature No. 2 of a C relay, such as relay 4C, to grounded source ofnegative potential of 24 volts, such as source 409. At the end of eachbreak signal, a timing circuit begins to function which, at the end ofabout three seconds, will operate a relay which will start thetransmission of the teletypewriter character test signals. lf less thanthree seconds occur between break signals, the timing circuit isrestored to its normal position. Thus for a succession of break signalswith less than three seconds between each breakf selector switch ZSWAwill continue to step. Three seconds after the last break signal, thetiming circuit will operate the R relay, such as relay lRl, which startsthe particular teletypewriting character test signal associated with theparticular contact with which the brush of stepping switch ZSWC isengaged.

After the R relay has operated to start the transmission of theteletypewriter character test signals, any subsequent break signal willcause the brush of the selector switch ZSWA to return to its zero ornormal position, stopping the transmission of teletypewriter charactertest signals. The circuit which operates on the break signals is timedso that the normal spacing intervals present in teletypewriter charactersignals do not operate it.

Production of Figures and H signals, followed by "RY signals with biasedor end distortion When four break signals are received from the linecircuit, selector switch ZSWA is operated to contacts Nos. 4 of both itsfront and rear banks and contacts Nos. 4 are so connected that theFigures signal is transmitted back over the line circuit. At the end ofthe Figures signal, the selector switch brush is automatically steppedto contacts Nos. 5, and contacts Nos. 5 are connected so that the signalfor the letter H is transmitted to the line circuit. At the end of the Hsignal, the selector switch brushes are automatically stepped to theircontacts Nos. 6, and contacts Nos. 6 are connected through a two-relaystepping circuit which alternates its condition at the end of eachteletypewriter character signal. The alternations are eiected by theupper armature of relay 3R which, when in its operated condition, causesthe signal for the letter R to be transmitted, and in its unoperatedcondition, causes the signal corresponding to the letter Y to betransmitted. The signal correspending to the letter R is transmittedwith 20 percent marking bias and the signal corresponding to the letterY is transmitted with 20 percent spacing bias, giving the effect of 20percent switched bias in the signals transmitted to the line circuit.

When the signals corresponding to the letters R and Y with 20 percentswitched bias are being transmitted to the line circuit, the receptionof a single break signal from the line circuit will step the selectorswitch ZSWA from contacts Nos. 6 to contacts Nos. 7, and will therebychange the switched bias to switched end distortion. The sending of asecond break signal will return the selector switch brush to its zeroposition, stopping the transmission of the teletypewriter character testsignals.

Function of a relay corresponding to` relay 4C or 5C,

each of which is individual to a teletypewriter character signal controlcircuit One selector control circuit is required for a telegraph centraloiice or switching center, one transmitter-distributor circuit isrequired for the transmitter-distributor (provided that the transmissionis at one speed), and one teletypewriter character signal controlcircuit is required at the telegraph central oice for each outlyingstation connected thereto.

Conductor 403 for signal control circuit 4CCC is connected to key 607and, likewise, conductor 501 for signal control circuit SCCC isconnected to key 608, both keys being located at the testboard 601 atthe telegraph central oftice. Relays 4R1, 4R2, 4K3 and 4R4 of signalcontrol circuit 4CCC are operated by key 607 whereby grounded source 609of negative potential of 24 volts is connected to conductor 403.Likewise, relays 5R1, SR2, 5R3 and 5R-4 of signal control circuit SCCCare operated by key 608 whereby grounded source 609 of negativepotential of 24 volts is connected to conductor 501. Each of signalcontrol circuits 4CCC and SCCC is set up, as will be hereinafterdescribed, to produce the sequence of teletypewriter character testsignals required for testing the SOTUS unit at the outlying station withwhich the particular signal control circuit is associated. Theconnection of source 609 of negative potential of 24 volts to either ofconductors 403 or 501 by the operation of its associated key alsooperates the respective relay of relays 4C, SC, etc., of signal controlcircuits 4CCC, SCCC, etc., and also by connecting source 609 of groundednegative potential to the windings of relays 4R1, 4R2, 4R3, 4R4 or ofrelays SR1, SR2, SRS, 5R4, or the corresponding relays of any of theother signal control circuits, prepares the particular signal controlcircuit for responding to the incoming break signals7 through theselector control circuit which is common to all the signal controlcircuits.

In the event that relay 4C becomes operated, grounded source 409 ofnegative potential of 24 Volts is connected over No. 2 armature andfront contact of the relay to a path extending over conductor 210, andthrough the windings of the stepping magnets ZSTPA and ZSTPB of selectorswitches 2SWA and ZSWB, respectively, to permit the subsequent operationof those stepping magnets.

Also, relay 4C, upon operating, connects at its No. 3 armature and frontcontact grounded source 409 to a path extending over conductor 405,through the winding of motor control relay 211 of distributor 2TD tostart the motor. It also connects the same source 409, over conductor405, through the winding of start magnet 212 of distributor 2TD topermit the subsequent operation of the start magnet when ground isconnected tothe other end of the winding of magnet 212 in a pathextending over conductor 21S, to ground at the front contact and outerlower armature for start relay SST, whereby the brush of distributor 2TDis allowed to rotate. Furthermore, relay 4C, when operated, connects atits No. 4 `armature and `front contact its respective grounded source401 of positive potential of 1S()` volts in a path extending overconductor 201, to thc inner ring of distributor 2TD, and at its No. 1armature and front contact closes a path extending over conductor 505 tothe plates, in parallel, of vacuum tubes SE1 and SBZ to produce 2Opercent bias and end distortion.

A summary of the functions of relay 4C or a similar relay, such as relay5C, is that the relay, upon operating, activates the selector switchesZSWA and 2SWB, it operates motor control relay 211, starts the motor ofthe distributor 2TD which is to be used for any one of the outlyingstations, it activates start magnet 212 of distributor 2TD for operationby the selector control circuit, it connects a source of positivepotential to the inner ring of distributor 2TD and it arranges theselector control circuit for bias and end distortion.

The purpose in subjecting the start magnet 212 of distributor 2TD tocontrol by the character signal control circuit relays, such as 4C,along with relay 211, is to ensure that whenever motor control relay 211of the distributor is released by the release of relay 4C, start magnet212 will also be released simultaneously, regardless of the condition ofthe selector control circuit, and the brush of the distributor 2TD willstop on the stop segment. The release of a relay, such as relay 4C, alsoremoves its grounded source, such as source 401, from the inner ring ofdistributor 2TD. These actions are taken to prevent the rotary brush ofthe distributor from stopping on a code segment, where it couldadversely atect the control of the signal control circuit 4CCC.

Function 07 the vacuum tube sending circuit When vacuum tube SBI isnon-conducting, the voltage at its plate is nearly the full voltage of1ts source, such as source 401, applied through variable resistor SP1and fixed resistor 3R23. This positive voltage at the plate of vacuumtube SBI is applied through resistor 3R24, to the grid of vacuum tubeSBZ, where it overrides the negative voltage applied through resistor3R25 from source S05 of negative potential of 130 volts, to make vacuumtube SBZ conducting.

When vacuum tube SBZ is conducting, the voltage at its plate will beabout 30 volts more positive than that at its cathode, or about 6 voltsof positive potential relative to ground. This small positive voltage,applied through resistor 3R27 to the grid of vacuum tube 3C1 isinsucient to override the negative voltage applied through resistor 3R23from grounded source S06 of negative potential and vacuum tube SClaccordingly is nonconducting. When vacuum tube SCI is non-conducting,the voltage at its plate from grounded source 307 through resistor 3R29is of a high positive potential. This positive voltage applied throughresistor 3R30 to the grid of vacuum tube SC2 overrides the negativevoltage of 130 volts from grounded source S08 through resistor 3R31 andaccordingly makes vacuum tube SC2 conducting.

When vacuum tube SC2 conducts, current flows from grounded source S09 ofa positive potential of 130 volts through resistor 3R32, plate andcathode of vacuum tube SC2, and the windings, in series, of relay SSD toground,

the current flowing through the windings of relay SSD is marking ineiect, and is approximately double the current flowing through the samewindings due to the connection of grounded source S10 of a negativepotential of volts, through resistor 3R15, which is spacing in etect.The armature of relay SSD is, therefore, held in engagement with itsmarking or left-hand Contact when vacuum tube SC2 is conducting. Whenvacuum tube SC2 is non-conducting, only the spacing current tiowing fromgrounded source S10, through resistor 3R15, is present in the windingsof relay SSD, and the armature accordingly is operated to its spacing orright-hand contact. The four vacuum tubes SB1, SBZ, SCI and SC2 are usedto permit adding bias and end distortion to the signals, as will behereinafter described.

In summary, when vacuum tube SBI is non-conducting, vacuum tube SBZ isconducting, vacuum tube SCI is nonconducting and vacuum tube SC2 isconducting, which operates relay SSD to its marking or left-handcontact. When vacuum tube SBI is made conducting, vacuum tube SBZbecomes non-conducting, vacuum tube SC1 becomes conducting and vacuumtube SC2 becomes nonconducting, which operates relay SSD to its spacingor right-hand contact.

Prodllclon of the frs! lelctjfpewrl'ter character fest signal of thetransmitter-start pattern in the leletypewrz'ter character signalcontrol circuit The opertaion of a key, such as one of keys 607, 608,etc., at testboard 601 operates the corresponding relay of relays 4C,5C, etc. As hereinbefore stated, the operation of either the relays 4Cor 5C, etc., conditions the corresponding signal control circuit foroperation. Assuming that signal control circuit 4CCC, associated withthe outlying station where the maintenance man is to test the "SOTUSunit, is activated by the operation of key 607, relay 4C is -accordinglyoperated. Relay 4C, upon operating, closes at its No. 3 armature andfront contact a circuit extending from `grounded source 409 of negativepotential, conductor 405, the winding of motor start relay 212 whichoperates to start the motor of distributor 2TD. In response to a singleincoming break" signal, selector switch ZSWA is operated, in a mannerwhich will be described hereinafter, to advance its brushes to its No. 1contacts on both its front and rear banks. Contact No. 1 on the frontbank connects vertical conductor V1 of all the signal control circuits4CCC, SCCC, etc. to the grid of vacuum tube SBI in a path extending overNo. l contact and brush of ybank No. 1 of stepping switch ZSWC, thebrushes of switch ZSWC occupying the positions shown in the idlecondition, conductors 205 and 206, contact No. 1 and brush of the frontbank of selector switch ZSWA, conductor 207, resistor 2R21, conductor204 to the vacuum tube grid. Contact No. 1 on the rear bank of switchZSWA closes an operating circuit for relay 4R1 which operates andprepares bank 4A of the signal control circuit 4CCC to transmit theteletypewriter signals of the transmitter-start pattern to start theteletypewriter transmitter at the outlying station. The operatingcircuit for relay 4R1 is traceable from grounded source 609 of negativepotential at the operated key 607, conductors 40S, 407 and 406, throughthe winding of relay 4R1, conductor 220, contact No. l and brush of therear bank of selector switch ZSWA, conductor S19, front contact andouter upper armature of start relay SST to ground.

Relay 4C, upon being operated at the time that the single break signalis received to operate start relay SST, closes a circuit from groundedsour 409 of negative potential, armature No. 3 and front contact ofrelayr 4C, conductor 405, through the winding of start magnet 212,conductor 21S, to ground at the front contact and outer lower armatureof start relay SST and distributor start magnet 212 operates to startthe distributor brush on its tirst revolution. When the distributorbrush rotates assagss over the start segment, grounded source 401 ofpositive potential is connected to a path extending over conductor 201,inner ring and start segment of distributor ZTD, conductor 202, resistor2R20, neon lamp 2N1, conductors S and 204 to the grid of vacuum tubeSBI. Normally, vacuum tube SBI is non-conducting due to the negativevoltage from grounded source S01 being connected through resistor 3R22to the grid of the tube, as hereinbefore described, vacuum tube SC2 isaccordingly conducting, and marking current is owing in the windings ofrelay SSD to operate that relay to its marking or righthand contact. Theconnection of the grounded sou-rce 401 of -a positive potential of 130volts overrides the negative potential of 130 volts from source S01 andvacuum tube SB1 starts conducting. When vacuum tube SBI becomesconducting, vacuum tube SC2 becomes nonconducting. With vacuum tube SC2non-conducting, marking current ceases to flow in the windings of relaySSD and spacing current now llows in the windings of that relay fromgrounded source 310 of negative potential to operate relay SSD to itsspacing or right-hand conductor.

When the rotating brush of distributor 2TD reaches code segment No. 1,the positive potential from grounded source 401 is connected in a pathextending over armature No, 4 and front contact of relay 4C, conductor201, inner ring, brush and segment No. 1 of distributor ZTD, conductors2P1 included in dot and dash line 214, front contact and armature No. lof relay 4R1, and to all the lamp sockets at the connections ofhorizontal conductor 4AH1 with vertical conductors V1 to 4V0 of bank 4A.No socket in any of the signal control circuits is effective to extend apath unless a neon lamp is inserted in such socket and only then at suchtimes as the brush of distributor 2TD is in engagement with the codesegment which corresponds to the horizontal conductor with which suchsocket is associated; for example, a neon lamp in a socket connected toconductors 4AH1 and V1, when the brushes of distributor 2TD engage theNo. 1 segment and the brush of bank No. l of stepping switch ZSWCengages the No. 1 contact. Conductor 2P1 is also connected to the frontcontact at armature No. 1 of relays 4R2, 4R3 and 4R4 as well as of eachof the four socket bank control relays of each of the other signalcontrol circuits of the system. The other conductors of those designated2P1 to ZPS, respectively, corresponding to the tive selecting pulses ofa tive-unit code signal, are respectively connected to the frontcontacts at armatures Nos. 2, 3, 4, and 5, of each of the socket bankcontrol relays in each of the signal control circuits.

Referring now to the selector control circuit, it wil-l be `assumed thatthe rotatable brush of bank No. l of stepping switch ZSWC is inengagement with contact No. 1. It will 'also be 'assumed that therotatable brush of the front bank of contacts of selector switch 2SWA isat contact No. 1 where it would actually be if one break signal had beenreceived over the line circuit from the outlying station. The rotatablebrush of contact bank No. 1 of switch ZSWC is now connected in a pathextending over conductor 206, contact No. 1 engaged by the rotatablebrush of the front contact bank of switch ZSWA, conductor 207, resistor2R21, conductor 204, to the grid of vacuum tube SE1. On contact bank No.l of stepping switch 2SWC, the path is extended over vertical con ductorV1 which is included in dot and dash line 402, to the lamp sockets yatthe interconnections of vertical conductor V1 and the respectivehorizontal conductors in socket banks 4A of the signal control circuit4CCC.

Considering the over-all connection which has been approached from bothdirections namely over horizontal conductor 4AH1 and Vertical conductorV1 of the signal control circuit 4CCC, the positive potential of 130volts from source 401 is applied over segment No. 1 of distributor ZTD,through a neon lamp 4A1-1 inserted in the socket at the inter-connectionof vertical conductor V1 and horizontal conductor 4AH1 of signal controlcircuit 4CCC if the first selecting pulse of the iirst test signal is tobe a spacing element. This positive potential of volts is furtherapplied to a path including contact No. 1 and brush of bank No. 1 ofstepping switch 2SWC, contact No. l and brush of the front ybank ofselector switch ZSWA and the grid of vacuum tube SBI, and normallynon-conducting vacuum tube SBI conducts. Consequently, normallyconducting vacuum tube SC2 becomes non conducting to cause relay SSD tosend a spacing puise to the line circuit.

When the brush of distributor 2TD reaches segment No. 2 the positivepotential of 130 volts from source 401 is connected through conductor2PZ included in the dot and dash line 214, to the front contact andarmature No. 2 of bank relay 4K1 of signal control circuit 4CCC tohorizontal conductor 4AH2. If no neon lamp is present in the socket atthe interconnection of vertical conductor V1 and horizontal conductor4AH2 of bank 4A', vacuum tube SBl will become nonconducting and vacuumtube SC2 will become conducting to operate relay SSD to its mark orleft-hand contact. A marking pulse is therefore sent to the linecircuit. If a neon lamp 4A1-2 is present in the lamp socket at theinterconnection of vertical conductor V1 and horizontal conductor 4AH2the positive potential of 130 volts from source 401 will be applied tothe grid of vacuum tube SBI, and vacuum tube SE1 will remain conductingand relay SSD will remain in its spacing position to send to the linecircuit a spacing pulse as selecting pulse No. 2 of the charactersignal.

As the brush of distributor 2TD passes over segments Nos. 3, 4 and 5,the positive potential of 130 volts from source 401 is connected throughthe front contacts and armatures Nos. 3, 4 and 5 of bank relay 4R1.Relay 4R1 prepares the connections of conductors 2P3, 2P4, and ZPSincluded in dot and dash line 215 over its front contacts and armaturesNos. 3, 4 and 5 to horizontal conductors 4AHS, 4AH4 and 4AH5,respectively. If a neon lamp 4A1-S is present in the lamp socket at theinterconnection of vertical conductor V1 and horizontal conductor 4AHS,the positive potential of 130 volts from source 401 is applied oversegment No. 3 of distributor 2TD when the brush passes over suchsegment, and will therefore be connected to the grid of vacuum tube SB1.Vacuum tube SE1 will become conducting, vacuum tube S02 will becomenon-conducting and relay SSD will transmit to the line circuit `aspacing pulse. If no neon lamp is present relay SSD will transmit to theline circuit a marking pulse for pulse No. 3. A similar performanceapplies to the situation when the brush passes over each of segmentsNos. 4 and 5 of the distributor 2TD. In the case of neon lamps 4A1-4 and4A1-5 being present in the other two sockets, Vertical conductor V1 willcause selecting pulses Nos. 4 and 5 of the character signal being sentto the line circuit to be spacing pulses and the absence of neon lampsat these intersections causes the corresponding pulses being transmittedto be marking pulses. When the brush of the distributor 2TD reaches thestop segment, no connection from this segment to the grid of vacuum tubeSBI is available. Vacuum tube SBI will therefore become non-conductingand vacuum tube SC2 will become conducting to cause relay SSD to send tothe line circuit a marking pulse during the time the distributor brushis in engagement with the stop segment at the end of each charactersignal. The engagement of the brush with the stop segment of distributor2TD causes, as hereinbefore mentioned, a positive potential of 130 voltsfrom source 401 to be extended over conductor 216, and resistor 2R35 tothe grid of vacuum tube 2D2, and vacuum tube ZDZ conducts to operaterelay 2P6 in connection with the production of the R and Y signals. Thisconnection has no significance at this time, because conductor 232 whichextends from the front contact of relay 2P6 terminates at the outerlower armature 1S of relay 3RY which is unoperated at this time, and thenoted armature has no connected back contact.

When the brush of distributor 2TD passes over segment No. 5 the positivepotential of 130 volts from grounded source 401 is impressed on thecircuit extending over conductors 2P5 and 217, resistor 2R23 to the gridof vacuum tube 2D1 and vacuum tube 2D1 becomes conducting to operaterelay ZPS. 1Relay ZPS', upon operating, connects at its armature andcontact a ground connection to a path extending over conductor 214,armature and back contact of relay SPH, upper armature and back contactof relay SRY, conductor 209, through the winding of stepping magnetZSTPC of stepping switch ZSWC, to grounded source 208 of negativepotential of 24 volts. Magnet ZSTPC operates, but brushes of steppingswitch ZSWC do not step until the stepping magnet releases. When thebrush of distributor 2TD passes off segment No. 5, vacuum tube 2D1becomes non-conducting and relay ZPS releases. Stepping magnet ZSTIC,upon releasing, advances the brushes of switch ZSWC.

Stepping switches of the type represented in FIG. 2 as switch ZSWCfrequently have double ended brushes, and the contacts of the switchbanks occupy arcs slightly less than 180 degrees, so that as one end ofthe brush is stepped out of engagement with the last contact of a bank,the other end of the brush advances into engagement with the firstcontact of the bank. In a full revolution of the brush the contacts of abank are traversed twice. It is possible to eliminate one of the twoarms of each brush so that while certain of the remaining arms aretraversing the contacts ofthe contact banks, the others are traversingthe opposite lSO-degree arc where there are no contacts. In the switchZSWC one of the two arms of each brush has been eliminated, and thearrangement is such that the brushes on contact banks l and 4 traversetheir contact banks concurrently in a half revolution of the brushes,and during the next half revolution the brushes associated with contactbanks 2, 4 and 5 traverse those contact banks. Only on bank No. l is theconnection to contact No. 2 significant at this time, in that itconnects the vertical conductor V2 for transmitting to the outlyingstation the second signal of the transmitter-start pattern.

The distributor brush, upon its next revolution over the start segment,will connect source 401 of positive potential directly through resistor2R20, neon lamp 2N1, conductors 203 and 204 to the grid of vacuum tube3B1 which again becomes conducting whereby relay SSD sends a spacingpulse to the line circuit. When the distributor brush arm passes overcoded segments Nos. 1 to 5, source 401 of positive potential will beconnected successively over conductors 2P1 to 2P5 included in dot anddash line 215, to the front contacts and armatures Nos. l to 5,respectively, of relay 4R1 to the lamp sockets connected at therespective interconnections of vertical conductor V2 and horizontalconductors 4AH1 to 4AH5 of the signal control circuit 4CCC. At thistime, however, the grid of vacuum tube 3B1 will be connected over thebrush on contact No. 1 in the front bank of selector switch ZSWA,conductors 206 and 205 to contact No. 2 on bank No. l of stepping switchZSWC. The effective connection of source 401 of positive potential overdistributor segments Nos. 1 to 5 will depend upon the presence of neonlamps in the tive sockets bridged between horizontal conductors 4AH1 to4AH5 and vertical conductor V2 of the signal control circuit. The secondcharacter signal to be sent to the line circuit is therefore determinedby the presence of neon lamps in one or more of tive sockets on verticalconductor V2 in lamp socket bank 4A', the presence of the lampsdetermining which of the selecting pulses of the character signal sentto the line circuit are spacing elements. At the end of the secondcharacter signal stepping magnet ZSTPC is again operated and released ashereinbefore described and the brushes of stepping switch 3SWC arestepped in their respective contact banks. When the brush of bank No. 1is on contact No. 3 of switch 3SWC the next character signal will bedetermined by the presence of neon lamps in the lamp sockets on verticalconductor V3, not shown, in socket bank 4A of the signal controlcircuit. This action continues as the brushes of the rotary steppingswitch 3SWC step over their respective banks, the brush of bank No. 1successively engaging each of the contacts between contact No. 3 andcontact No. 20 on bank No. 1. Each of the contacts from No. 4 to No. 20of bank No. l are connected to vertical conductors V4 to V20,respectively, of the signal control circuit. Vertical conductors V5, V6,V10, V15, V19 and V20 of this group are shown, it being understood thatthe intermediate vertical conductors are also furnished with theirrespective lamp sockets at each of the intersections with the horizontalconductors 4AH1 to 4AHS. Contacts Nos. 21 and 22 of bank No. 1 ofstepping switch 3SWC are left blank and therefore no vertical conductorsare provided in the signal control circuits for these contacts.Accordingly when the brush of bank No. l is on either of contacts 2l or22 the tive selecting pulses delivered to the grid of vacuum tube 3B1during the time the brush of distributor 2TD is rotating over codedsegments Nos. l to 5, are marking to send marking pulses correspondingto Letters signal, to the line circuit.

Immediately after the brush of stepping switch 2SWC passes off contactNo. 22 of bank No. 1 the brush on bank No. 2 engages contact No. l ofbank No. 2. This contact is connected to vertical conductor No. 2l ofthe signal control circuits and the character signal sent to the linecircuit at this time will, as hereinbefore described, be determined bythe neon lamps being present in the lamp sockets on vertical conductorV21 at the intersections of conductors 4AH1 to 4AHS. As the brushes ofstepping switch ZSWC continue to step the brush on bank No. 2 reachesits contact No. 20 of bank No. 2 which is connected to verticalconductor V40 of the signal control circuits. Contacts Nos. 2l and 22 ofbank No. 2 of the stepping switch ZSWC are also left blank and theLetters signals are sent to the line circuit while the brush of switchZSWC engages each of these contacts. When the brush of stepping switchZSWC passes off contact No. 22 of bank No. 2, the brush of bank No. lreaches Contact No. l of this bank, and the sending of the sequence ofcharacter signals of the transmitter-start pattern is repeated to theline circuit until other break signals are received from the outlyingstation.

In response to two break signals from the outlying station, as will bedescribed hereinafter, the brushes of selector switch ZSWA step to theirrespective No. 2 contacts and an energizing circuit for control relay4R2 of bank 4B is closed and that for control relay 4R1 of bank 4A isopened. Relay 4R1 releases and relay 4R2 operates and the tive codesegments of distributor 2TD then are connected to the verticalconductors V1 to V40 successively in the lamp socket bank 4B. Therefore,an entirely new set of character signals can be produced by thearrangement of the neon lamps in the `lamp socket bank 4B.

This new set of signals represents the receiver cut-on pattein or aportion thereof for that outlying station which is at the time connectedto its signal control circuit 4CCC. Therefore, in response to two breaksignals from the outlying station, relays 4R2, 4R3 and 4K4 are operatedin turn, and during the operation of each, the ve code segments ofdistributor ZTD are connected to vertical conductors V1 to V40successively in their respective lamp socket banks 4B', 4C and 4D. Thecircuits for operating relays 4K2, 4R3 and 4K4 will be hereinafterdescribed under Selector Control Circuit.

DESCRIPTION OF SELECTOR CONTROL CIRCUIT The selector control circuitpermits the selection of the J17 various teletypewriter character testsignals by the sendiugof the break signals `from the outlying station tothe line circuit. The signals obtainable and the number of break signalsrequired for each are as follows:

Type o Signal Number of Break Signals signal.

When any signals except the alternate R and Y signals with 20 percentswitched bias are being received, the sending of one break signal willstop the transmission -rom a signal control circuit. When the alternateR and Y signals with switched bias are being transmitted, the rstincoming break signal will change the switched bias to switched enddistortion, and the next incoming break signal will stop thetransmission.

Relay 3REC of the selector control circuit is connected in the samemanner as relay SSD on a diierential loop repeater basis, the apex ofthe windings of relay 3REC being connected to the armature of relay 3SD,with one winding of the relay being connected through resistor 3R16 ofresistance value of 4000 ohms, to ground, as the biasing winding, andthe other winding identied as the line winding, bein-g connected throughvariable resistor SP5, and then over the tip conductor 311 tothe tipspring of jack 621 at testboard 601 from where it can be patched bymeans of cord circuit 610 to a line circuit extending to any one of theoutlying stations, such as stations 602 and 603. Source 312 of positivepotential of 130 volts is connected by means of ring conductor 313 to`the ring spring of jack 621 to permit the connection to the jack of aline circuit having no other source of potential and extending to anyone of the outlying stations.

Relay 3REC is normally held operated to marking by the Iloop current ina circuit extending from source 314 to negative potential of 130 voltsmarking or left-hand contact and armature of relay l38D, conductor 315,through the upper winding of relay 3REC, resistor SP5, conductor 311,tip spring in its normal position of jack 621 to source 611 of positivepotential of 130 volts at Itestboard 601. Relay SREC releases onincoming break signals from the outlying station but is not responsiveto spacing pulses of the outgoing teletypewriter signals because thecurrent through the biasing winding holds it on marking. 'Relay 3RECoperates suciently fast to follow the teletypewriter signals incomingover the line circuit. Relay 3REC, in its marking condition, completes acircuit from its grounded armature and marking or left-hand contact,conductor 316, through the winding of slow-release relay 3LS, resistor3K3, to source 317 of positive potential of 130 volts, and relay 3LS,which is identilied herein as the Long Space relay, is normally heldoperated. When relay -3REC releases due to a spacing pulse of ateletypewriter signal incoming over the line circuit, its groundedarmature becomes `disconnected Ifrom the winding of relay 3LS butcurrent continues to flow in the winding of relay 3LS inasmuch ascondenser 3c1 is in a charged condition. When the charge on condenser3c1' decreases to a value such that the current iowing is insucient tohold relay 3LS operated, relay 3LS releases. The time interval of thisrelease is suiciently great that the longest spacing impulse of ateletypewriter signal, such as is had in the blank signal, is notsuiiicient in length to allow relay 3LS to release. 'I'hus in responseto incoming teletypewriter signals, relay 3LS remains operated whilerelay 3REC follows the signals. A break signal on the line circuit willbe of suicient duration to allow relay 3LS to release. Relay 3LS, uponreleasing, connects ground at its lower armature and back contact, to acircuit extending over the inner lower armature and back contact ofstart relay 3ST, conductor 304, through the winding of stepping magnetZSTPA, conductor 210, front contact and armature No. 2 of relay 4C whichwill be in operated condition at the time, to source 409 of negativepotential of 24 volts. Stepping magnet ZSTPA operates to step thebrushes of the front and rear banks or selector switch ZSWA to theirrespective No. l contacts. Selector switch ZSWA, upon operating, opensits olf-normal contact 218 to disconnect ground from a circuit extendingover conductors 219 and 318, resistor 3R6, condenser 302 to ground,while the ground connected at the upper armature and back contact ofrelay 3LS is still connected to cendenser 362'.

Relay 3REC, upon reoperating to its marking or normal condition at theend -of a break signal, reoperates relay 3LS. Relay 3LS, upon operating,disconnects ground at its upper armature and back contact from condenser302 and this condenser starts to charge in a path extending fromgrounded source 339 of positive potential of volts, resistor 3R4,conductor 318, resistor 3R6, condenser 3c2, to ground whereby condenser3c2 is charged with a positive voltage. If no further break signals larereceived from the line circuit, the charge on cendenser 3c2 becomessuiicient in about 3 seconds to cause cold cathode tube 3A to fire, andrelay 3ST operates in an obvious circuit.

Relay 3ST which is identified herein as a start relay, upon operating,(l) closes at its inner upper armature and front contact a locking pathfor itself, traceable over conductor 333, to ground at the lower contactof olfnormal contact 218 of selector switch SSWA, the brushes of whichare now operated to their No. l contacts; (2) connects ground on itsouter lower armature and front contact to a circuit traceable overconductor 213, through the winding of start magnet 212, conductor 405,front contact and armature No. 3 of lany one of relays 4C, 5C, etc.,whichever of these relays is operated in response to the operation ofits respective selective, key of keys 607, 608, etc., then to `agrounded source, such as source 409, of negative potential of 24 volts,and start magnet 212 operates to release the brush of distributor 2TD tothereby start rotation of the brush (the motor of distributor ZTD isoperating lat this time since motor relay 212 was operated when the keycontrolled relay of relays 4C, 5C, etc., was operated); (3) connectsground at its outer upper armature and front contact in a circuittraceable over conductor 319, brush on its contact No. l of the rearbank of selector switch ZSWA, conductor 220 included in dot `and dashline 224, through the winding of relay 4R1, conductors 406, 407 and 403,an operated key of keys 607, 608, etc., to grounded source 609 ofnegative potential of 24 volts at the testboard and assuming that key607 is operated, relay 4R1 operates; and (4) prepares at its inner lowerarmature iand front contact a path which will close when relay 3LS againreleases, the path when closed extending from ground at the lowerarmature and back contact of relay 3LS, inner lower armature and frontcontact of relay 3ST, conductor 320, inner lower amature and backcontact of relay 3RY, conductor 321, through the winding of releasemagnet 3RLSA, conductor 210, front contact and armature No. 2 of relay4C, to source 409 of negative potential of 24 volts. Now any subsequentrelease of relay 3LS due to a break signal will cause release magnetZRLSA to release whereby the brushes of stepping switch ZSWA return tozero position.

The operation of relay 4R1 connects the circuits from the tive-codeelement segments of the distributor 2TD through conductors 2P1 to ZPSincluded in dot and dash line 215 to horizontal conductors 4AH1 to 4AH5,respectively, of lamp socket bank 4A of signal control circuit 4CCC.Thus the Yarrangement of neon lamps in the sockets at theinterconnections of the horizontal conductors 4AH1 to 4AH5 and `verticalconductor V1 of the character signal control circuit will determine themarking and spacing pulses of a character signal to be sent by relay 3SDto the line circuit.

The ground furnished at the armature and spacing or right-hand contactof relay SREC at the time that relay is in the spacing condition willhold relay 3ST operated in a circuit traceable over conductor 322, innerupper armature and front contact of relay 3ST, resistor 3R8, through thewinding of relay 3ST, resistor 3R9, to grounded source 323 of positivepotential of 130 volts. Relay 3ST is, therefore, held operated during areceived break signal even though the ground from the oi-normal contacts218 has been removed by the return of the brushes of selector switch2SWA to their zero position. This prevents relay 3ST from releasing andtransferring the ground at the armature of relay 3LS back to the windingof stepping magnet 2STPA of selector switch 2SWA, which would cause theselector switch to step again to contact No. 1.

With relay 3ST operated, the sending of teletypewriter signals by relaySSD will take place, since the start magnet 212 of distributor 2TD isoperated, and with relay 4R1 operated, the signals will be derived fromthe dispositions of neon lamps in the sockets connected to conductors4AH1 to 4AH5. The teletypewriter character signals produced by the neonlamp arrangements on each of the vertical conductors in lamp socket bank4A' constitute the testing signals for esing the transmitter startfeature of a SOTUS unit at the calling-in outlying station. This testingsignal material involves a pause after the transmission of a blanksignal which will be about three character signals in duration. Thispause is obtained as follows: The stepping of the brush to contact No. lon the rear bank of switch 2SWA connects ground at the outer upperarmature and front contact of relay 3ST to the winding of relay 4R1 ashereinbefore described. From this same contact No. 1 the groundconnection at the outer upper armature and front contact of relay 3ST isconnected over conductor 220 to the brushes on contact banks Nos. 4 and5 of stepping switch 2SWC. When the brush of contact bank No. 4 ofstepping switch 3SWC passes over contacts Nos. 2 to 4, inclusive, 7 to9, inclusive, l1, 12 and 16 to 18, inclusive, and also the brush ofcontact bank No. of the same stepping switch passes over thecorresponding contacts of contact bank No. 5, this ground is connectedto the junction of resistor 2R20 and neon lamp 2N1. When this ground isso connected, the source 401 of positive potential of 130 volts, whichis normally connected to the grid of vacuum tube 3B1 during the time thebrush of distributor 2TD is at the start segment, is shunted out andneon lamp 2N1 does not tire, so that vacuum tube 3B1 remains cut olf andno space pulse is transmitted at this time. It in lamp socket bank 4A nolamps are provided for the character signal to be sent at the timecorrespending to engagement of brushes of contact banks Nos. 4 and 5 ofstepping switch 2SWC with each of the above enumerated contacts of theirrespective banks, no spacing pulses at all will be sent to the linecircuit, and a continuous marking pause will occur on the line circuitfor the duration of the character signal. Therefore, after three or fourconsecutive intervals transpire in this manner during which the brushesof stepping switch 2SWC are passing over the noted contacts of contactbanks Nos. 4 and 5, and no lamps are provided in the lamp socketsassociated with the vertical conductors V1 to V40 served in thecorresponding contacts of contact banks Nos. l and 2, a steady markingpause of three or four character signals in duration will be produced.

Vertical conductors V1 to V40, considered now with 20 respect to lampsocket bank 4A' only, are associated with contacts Nos. l to 20 ofcontact bank No. 4 and contacts Nos. 1 to 20 on contact bank No. 5 ofstepping switch 2SWC, and are arranged for characters as follows:

Vertical Lamp Socket Contacts on Banks Conductors Nos. 4 and 5 of SwitchCharacter Signals 2SWC Vl and V21 Contacts No. 1 and Blank (lamps in No. l.. socket positions 4AH1 to 411115, lnelusive).

V2 to V4 and V22 to Contacts Nos. 2 to 4 and Nos. 2 to 4.

N o lamps (pause).

V5 and V25 Contacts No. 5 and Space (lamps ln N o. 5. socket positions4AH1, iai-t2, 41.113 and 4AH5). V6 and V26 Contacts No. 6 and "H(non-valid code No. 6. signal) (lamps in socket positions 4AH1, LAI-I2,4AH3 and 4AH5). V7 to V9 and V27 to Contacts Nos. 7 to 9 No lamps(pause).

V29. and Nos. 7 to 9. V10 and V30 Contacts N o. l0 and Valid codesignal.

V11, V12 and V31, V32.

No. 10. Contacts Nos. 11 and g and Nos. 11 and Contacts Nos. i3 andPause.

Nota-Contacts Nos. 21 and 22 in each of banks Nos. 4 and 5 of steppingswitch 2SWC are not connected to the neon lamp sockets and, accordingly,the Letters signal will be sent when the brushes of stepping switch 2SWCare on contacts Nos. 21 and 22 of banks Nos. 4 and 5.

When the brush of stepping switch 2SWC is on contact No. 14 or 22 ofeither bank No. 4 or 5, the ground on the brush is connected to thewinding of release magnet ZRLSA of selector switch 2SWA and releasemagnet ZRLSA operates to reset the brushes of that selector switch tonormal and stop the transmission of teletypewriter test signals. Thusafter each teletypewriter signal combination of a non-valid and validtransmitter start pattern and after the stop code signal has been sent,the transmission of teletypewriter test signals will stop. When it isdesired that the transmission of teletypewriter signals resume, they arerestarted by again sending one break signal. It will be apparent that atest should not be ended with the brush of either bank No. 4 or 5 ofswitch 2SWC engaging contact No. 14. A break signal should betransmitted which will effect transmission of the stop code signal andcompletion of the stepping switch cycle.

Receiver cut-on teletypewriter character lest signals The receivercut-on teletypewriter character test signal combinations are obtained bysending from the outlying station two break signals over the linecircuit. These break signals step the brushes of stepping switch 2SWA,as hereinbefore described, to contact No. 2, and approximately 3 secondsafter the end of the second break signal, cold cathode tube 3A fires tooperate relay 3ST. Relay 3ST, upon operating, closes the operatingcircuit for start magnet 212 of distributor 2TD and the brush ofdistributor 2TD again starts to rotate for another series of revolutionsas hereinbefore described.

When the brush on the front bank of selector switch ZSWA steps tocontact No. 2, the connection is the same as when the brush was oncontact No. 1, which connects the grid of vacuum tube 3B1 to the brusheson contact banks Nos. l and 2 of stepping switch 2SWC and the grid ofvacuum tube 3B1 receives the pulses of the coded signals from the lampsocket banks 4B', 4C', and 4D'in turn, through contact banks Nos. 1 and2 successively of stepping switch ZSWC, conductor 206, contact No. 2 ofthe front contact bank and brush of selector switch 2SWA, conductor 207,resistor 2R21, conductor 204, to the grid of vacuum tube 3B1.

The operation of relays 4R2, 4R3 and 4R4, as hereinbefore stated, willnow be described in detail. When the brush of the rear contact bank ofselector switch 2SWA is on contact No. 2, ground at the outer upperarmature and front contact of relay 3ST is connected over conductor 319,brush and contact No. 2 of the rear contact bank of selector switch2SWA, to the brush of contact bank No. 3 of stepping switch 2SWC, andthis ground is also connected over conductor 225, through the oit-normalcontact 226 of stepping switch 2SWB in its normal position, to conductor221 included in dot and dash line 224, through the winding of relay 4R2,conductors 406 and 407 and conductor 403 through key 607 in operatedcondition to grounded source 609 of negative potential of 24 volts andrelay 4R2 operates. Relay 4R2, upon operating, connects the tive code orselecting segments of distributor 2TD to lamp socket bank 4B'. 'I'heteletypewriter character signals transmitted from lamp socket bank 4B atthis time will, therefore, be determined by the arrangement of the neonlamps in the sockets of bank 4B. When all the signals determined by thelamp arrangement on each of the Vertical conductors V1 to V40 of lampsocket bank 4B have been transmitted, each signal causing steppingmagnet 2STPC to operate and release, the brush of bank No. 3 has beenstepped around through an angular distance of approximately 360 degreesand s then in engagement with its contact No. 22.

When the brush of contact bank No. 3 of stepping switch 2SWC reachescontact No. 22, it closes a circuit extending from the ground onconductor 319 over the brush and rear bank contact 2 of stepping switch2SWA, over conductor 227, through the winding of stepping magnet 2STPB,conductor 210, front contact and armature No. 2 of relay 4C, to groundedsource 409 of negative potential of 24 volts. Stepping magnet 2STPBoperates, and the brush of selector switch 2SWB now takes its rst stepto contact No. 1. When the brush arm of selector switch 2SWB reachescontact No. l, the operating circuit of relay 4R2 is opened atoil-normal contact 226 and relay 4R2 releases. At contact No. l ofselector switch 2SWB, a new circuit is closed from conductor 225 eX-tending over conductor 222 included in dot and dash line 224, throughthe winding of relay 4R3, conductors 406, 407 and 403, through theoperated key 607, to ground source 609 of negative potential of 24 Voltsand relay 4K3 operates. Rel-ay 4R3, upon operating, connects the ve codesegments of distributor 2TD to lamp socket bank 4C. The teletypewritercharacter signals transmitted through lamp socket bank 4C to theoutlying station will now be determined by the arrangement of the neonlamps in each of vertical conductors V1 .to V40, in turn, of lamp socketbank No. 4C.

When the brush on contact bank No. 3 of stepping switch ZSWC againreaches contact No. 22, it connects ground again to the winding ofstepping magnet 2STPB of selector switch 2SWB causing the brush ofswitch 2SWB to step to contact No. 2. This removes the ground from theoperating circuit of relay 4R3 which releases and with brush on contactNo. 2 of selector switch 2SWB, a circuit is closed over conductor 1223included in dot and dash line 224, through the winding of relay 4R4,conductors 407 and 403, the operated key 607, to grounded source 609 ofnegative potential of 24 volts and relay 4R4 operates. Relay 4R4, uponoperating, connects the tive code segments of distributor 2TD to lampsocket bank 4D. The teletypewriter character signals sent at thistimefrom lampsocket bank 4D to the outlying sta- 22 tion'willl now bedetermined by the arrangement of the neon lamps of lamp socket bank 4D'.

When the brush on contact bank No. 3 of stepping switch 2SWC reachescontact No. 22 the next time, it will operate stepping magnet 2STPBwhereby the brush of selector switch 2SWB is stepped to contact No. 3wherefthe ground is connected to the winding of release magnet ZRLSBwhich operates to restore the brush of selector switch 2SWB to normal.The brush of selector switch 2SWB upon being restored to normal, that isto its zero position, removes ground from the operating circuit forrelay 4R4 thereby releasing the'relay. Thus the teletypewriter charactersignal transmitting circuit is capable of sending a total of charactersignals determined by the three lamp socket banks 4B', 4C and 4D. Whenthe brush of selector switch 2SWB is restored to normal, groundedconductor 319 is again connected over the brush and No. 2 contact of therear bank of selector switch 2SWA, conductor 225, off-normal contacts226,

conductor 221 included in dot and dash line 224, through the winding ofrelay 4R2, conductors 4P1, 407 and 40'3, operated key 607, to thegrounded source `609 of negative potential of 24 volts and relay 4R2again operates. The teletypewriter character signals are againtransmitted to the outlying station as determined by the neon lamps inlamp socket bank 4B. In this manner the teletype writer character testsignals of the receiver cut-on code are repeated to the outlyingstation. The sending of the signals of the receiver cut-on pattern willcontinue until a break signal is transmitted from the outlying-stationwhich will reset the brush of selector switch 2SWA to its normal or zeroposition and stop the transmission of teletypewriter signals.

Operation of testboard calling-in signal The testboard calling-in signalis operated by sending three break signals. These signals step thebrushes of selector switch 2SWA to their respective contacts No. 3. Withthe subsequent operation of relay 3ST as hereinbefore described, theground connected at the outer upper armature and front contact of relay3ST is extended over conductor 319, brush in engagement with contact No.3 on the rear contact bank of `selector switch 2SWA, conductor 228,through lamp 612, to grounded source 613 of negative potential of voltsand the calling-in signal lamp 612 at the testboard operates to indicateto the attendant at the testboard that he is wanted in a telephoneconnection with the maintenance man at the outlying station. Theattendant at the testboard upon observing the lighting of calling-insignal lamp removes the patching cord from jacks 621 and 616 and insertsplug 614 of his telephone headset 615 into jack 616 and is now intelephonie communication with the maintenance man at the outlyingstation whereat the maintenance man after sending the three breaksignals to operate the calling-in signal lamp inserts plug 617 of hisset 619 into jack 618. The maintenance mans telephone set `619 is nowconnected through to the telephone headset of the attendant at thetestboard. The transmission of a break signal by either the maintenanceman or the attendant at the testboard will restore selector switch 2SWAto its normal position. The restoring circuit is traceable from groundedsource 409 of negative potential of 24 volts, armature No. 2 and frontcontact of relay 4C, conductor 210, through the winding of releasemagnet ZRLSA, conductor 321, back contact and inner lower armature ofrelay SRY, conductor 320, front contact and inner lower armature ofrelay 3ST, to ground at the back contact and lower armature of relaySLS'.

Production of alternate R and Y signals Figures, H and then alternate Rand Y signals with 20 percent switched bias are obtained by sending fourbreak signals from the outlying station to the line circuit. The fourbreak signals step the brushes on selector switch V2SWA to theircontacts No. 4, whereupon relay 3ST operates as hereinbefore described.With the brush of the front contact `bank of selector switch ZSWA oncontact No. 4, the grid of vacuum tube 3B1 is connected over conductor229, through neon lamp 2N10, conductor 2P3, to code segment No. 3 ofdistributor 2TD. With this connection, only selecting pulse No. 3 willbe spacing when the brush rotates over distributor 2TD to send theteletypewriter character signal for Figures to the line circuit. Withthe brushes of selector switch ZSWA on their contacts No. 4 the brush ofthe rear contact bank connects grounded conductor 319 to a pathtraceable over conductor 230, through the winding of Figures H relay3FH, resistor 3R10, to grounded source 324 of positive potential of 130volts, thereby operating relay 3FH. Relay 3FH, upon operating, transfersat its armature, conductor 214 to a path extending over conductor 304,through the winding of stepping magnet ZSTPA, conductor 210, frontcontact and armature No. 2 of relay 4C, to grounded source 409 ofnegative potential of 24 volts. Conductor 214 extends in the oppositedirection to the front contact of relay ZPS. Relay QPS operates inresponse to the selecting pulse received from code segment No. 5 ofdistributor 2TD and thereby during the operation of relay ZPS connectsground momentarily to operate stepping magnet ZSTPA. Therefore, at thebeginning of selecting pulse No. 5 stepping magnet 2STPA operates tostep the brushes of selector switch ZSWA to their respective contactsNo. 5.

With the brush of the front contact bank of selector switch ZSWA at itscontact No. 5 the grid of vacuum tube 3B1 is connected in a circuittraceable over circuit 204, resistor 2R21, conductor 207, brush oncontact No. 5 of selector switch ZSWA, through neon lamps 2N7, 2N8 and2N9, in parallel, and over their respectively associated conductors 2P1,2PZ and 2P4 to the code segments Nos. l, 2 and 4 and inner ring ofdistributor ZTD, conductor 201, front contact and armature No. 4 ofrelay 4C, to grounded source 401 of positive potential. When the brushof the distributor 2TD rotates over segments Nos. l, 2 and 4 thecorresponding pulses will be transmitted to the line circuit as spacingelements of the character signal H. The fifth selecting pulse of thecharacter signal H, operates relay ZPS which upon operating, will stepthe brushes of selector switch ZSWA to their respective contacts No. 6.

The stepping of the brush on the rear contact bank of selector switchZSWA to contact No. 6 causes the release of relay SPH but condenser 3c4'has stored a charge which delays the release of the relay sufficientlyso that a positive operation of the stepping magnet ZSTPA occurs beforethe circuit to the stepping magnet 2STPA is opened. The same brush ofselector switch 2SWA on its contact No. 6 closes a circuit from groundedconductor 319 extending over conductor 231, through the winding of relay3RY, resistor 3R11, to grounded source 325 of positive potential of 130volts and relay 3RY operates.

Relay 3RY upon operating, opens at its upper armature and back contactthe operating circuit of stepping magnet 2STPC of stepping switch 2SWCso that the stepping switch does not operate during the sending of altennate R and Y signals. Also, relay 3RY upon operating, transfers itsinner lower armature from its back contact, where it opens the operatingcircuit for release magnet ZRLSA, to its front contact, where it closesa path extending over conductor 304, through the winding of steppingmagnet 2STPA, conductor 210, front contact and armature No. 2 of relay4C, to grounded source 409 of positive potential. Stepping magnet 2STPAoperates to step the brushes of selector switch 2SWA to their respectivecontacts No. 7. This is `for the purpose of making it easy to change thesignals from the alternate R and Y signals with 20 percent switched biasto alternate R and Y signals with 2O percent switched end distortionwhich will be hereinafter described.

The stepping of the brush of the front contact bank of selector switchZSWA to contact No. 6 connects the grid of vacuum tube 3B1 to the upperarmature of relay 3R. When relay 3R is in its released position the gridof vacuum tube 3B'1 is therefore connected over conductor 334, upperarmature and back ycontact of relay 3R, conductor 326, through neonlamps 2N5 and 2N6, in parallel, their respective conductors 2PZ and 2P4and the code segments Nos. 2 and 4 of distributor 2TD, to transmit tothe line circuit a Y signal comprising spacing elements for pulses Nos.2 and 4 and marking elements Vfor pulses Nos. l, 3 and 5. When relay 3Ris in its operated condition the grid of vacuum tube 3B1 is connectedover conductor 327, through neon lamps 2N2, 2N3 and 2N5 in parallel, tothe respective conductors 2F11, 2P3 and 2P5 and the code segments Nos.l, 3 and 5 of distributor ZTD to transmit to the line circuit an Rsignal comprising spacing elements for pulses Nos. 1, 3 and 5 andmarking elements for pulses Nos. 2 and 4. Thus if relay 3R is arrangedto alternately operate on one character signal and to release on thenext, a succes sion of alternate R and Y signals will be transmitted tothe line circuit.

Relay '3RY upon operating, also prepares, for closure during the timethat the brush of distributor 2TD is on its stop segment, a pathextending yfrom ground at the armature and front contact of relay 2P6,conductor 232, outer lower armature and front contact of relay 3RY,conductor 329, to the path comprising relays 3R and 3Y, during the stoppulse of each character signal transmitted at this time to the linecircuit. When the ground at the armature and front contact of relay 2P6,as applied to the path comprising relays 3R and 3Y, is applied throughthe break contacts controlled by the lower :armature to the winding ofrelay 3R, relay 3R operates and locks to ground at its inner lowerarmature and front contact. No operation of relay 3Y can occur at thistime because the ground pulse applied to the path comprising relays 3R:and 3Y is connected through the lower armature and back contact ofrelay 3Y, resistor SR2, to -grounded source 328 of positive potential ofvolts whereby the winding of relay 3Y is shunted. At the end of the stoppulse of the signal transmitted to the line circuit, when relay 2P6releases, ground is removed at lthe armature and front contact of relay2P6 in the circuit traceable over conductor 232, outer lower armatureand Contact of relay 3RY, conductor 329, to the path comprising relays3R and SY and relay 3Y will operate in a path traceable from -groundedsource 328 of positive potential of 130 volts, resistor SR2, through thewinding of relay 3Y, front contact and inner lower armature of relay 3Rto ground. Both relays 3R and 3Y are now operated. The character signalsent while relay 3R was unoperated was a Y signal. With relay 3R nowoperated the next character signal will be an R signal. At the end ofthis character signal the ground pulse applied to the path comprisingrelays 3R and 3Y by the operation of relay 2P6 will be connected overthe inner lower armature and front contact of relay 3Y, resistor 3R1, togrounded source 328 of positive potential and the winding of relay 3R isthereby shunted and relay 3R releases. Relay 3Y will remain operated dueto the fact that the ground pulse received over conductor 329 is nowapplied over the make-before-break contacts of relay 3R, through thewinding of relay 3Y, resistor 3R2, to grounded source 328 of groundedpositive potential. The removal of the ground pulse on conductor 1329 atthe end of stop pulse of the R character signal will cause the releaseof relay 3Y and both relays will now be released. With relay 3R nowreleased, the character signal sent to the line circuit will be a Ysignal. The circuit comprising relays 3R and 3Y continues to operate asjust described, one operation of relay 2P6 connecting a ground pulse tothe circuit to operate relay 3R at the beginning of the pulse and relay3Y at the end of the pulse. The ground pulse applied during the nextcharacter signal releases relay SR at the beginning of the pulse andreleases relay SY at the end of the pulse. Thus relay SR causes R and Ysignals to be alternately transmitted-to the line circuit.

Operation of switched bias and switched end distortion circuit Thetransition delay required to produce bias or end distortion is 'had inresponse to the operation and release of relay SR by connectingcondenser S07 associated with relay SED to the plate of either vacuumtube SB1 or SBZ, `where it delays the operation of 'relay SSD eitherfrom marking to spacing or lfrom spacing to marking. Switched bias isobtained by switching the condenser from vacuum tube SB1 to SBZ duringthe stop pulse of each character signal transmitted to the line circuit,while switched end distortion is obtained by switching the condenserfrom one vacuum tube to the other during the start pulse of eachcharacter signal. A detailed description of this operation is asfollows: When relay SED is released the circuit will produce switchedbias and when it is operated, switched end distortion will result. Whenrelay SED is released, condenser Sc7 is connected in a path traceableover the left-hand armature and back contact of relay SED, outer lowerarmature and back contact of relay SR, conductor S30, to the plate ofvacuum tube SB1. Vacuum tube SB1 is non-conducting during a markingpulse and while it is in this condition condenser Sc7 is charged to apositive potential of nearly 130 volts in a path traceable from groundedsource 401 of positive potential, armature No. l and front contact ofrelay 4C, conductor 505, variable resistor SP1, resistor 3R23, conductorS30, back Contact and outer lower armature of relay SR, back contact andleft-hand armature of relay SED, condenser Sc7', to ground. When vacuumtube SB1 becomes conducting due to a positive voltage re ceived at itsgrid, condenser 3c7' discharges through the relatively low impedance ofvacuum tube SB1 during its conducting interval and very little delay inthe markngl to-spacing transition of relay SSD occurs. When the positivevoltage is removed from the grid of vacuum tube SB1 and it becomesnon-conducting, condenser Sc7 charges to a positive potential at a ratedetermined by the resistance in the plate circuit of vacuum tube SB1.This resistance is determined by the setting of variablere4 sistor SP1.The time required for condenser Sc7' to become charged to a potentialsucient to cause the followf ing vacuum tube SBZ to conduct again, isthe time interval by which the operation of relay SSD from spacing backto marking is delayed. This time interval is thus a measure of thespacing bias produced in the signals by the delay in thespacing-to-marking transition. The connection of condenser Sc7' to theplate of vacuum tube SB1 takes place when relay SR is released, underwhich condition a Y signal is sent to the line circuit. 'I'herefore a Ysignal is sent with the spacing bias. When relay SR is operated to causethe sending of an R signal, the operation of its outer lower armature toits front contact transfers condenser Sc7' to the plate of vacuum tubeSBZ. Vacuum tube SBZ is conducting for marking and non-conducting torspacing During fa spacing-to-marking transition, `vacuum tube SBZ goesfrom non-conducting to conducting, and condenser S07 discharges throughvacuum tube SBZ, causing no delay in the transition. During amarking-to-spacing transition vacuum tube SBZ goes from conducting tonon-conducting condition. At this time condenser Sc7 charges slowly to apositive potential lat a rate determined by the resistance at which thevariable resistor SPS is set. The marking-to-spacing transition is thusdelayed. A delay in the marking-to-spacing transitions has the samerelative effect on the elements of a teletypewriter character signal asan advance in the spacing-to-marking transitions, and accordinglyproduces marking bias. The connection of condenser Sc7' to the plate ofvacuum tube 26 SBZ therefore applies marking bias to the signalstransmitted to the line circuit. rl`he signals corresponding 'to theletter R are therefore subjected to marking bias while the signalscorresponding to the letter Y is biased to spacing The summary of theoperation of the biasing circuit is that as relay SR operates andreleases to cause sending of, tirst, an R signal and then a Y signal,condenser Sc7 is transferred back and forth between the plates of vacuumtubes SB1 and SBZ, applying spacing bias to the Y signal when thecondenser is connected to rthe l plate of vacuum tube SB1, and markingbias to the R signal when it is connected tothe plate of vacuum tubeSBZ. It should be noted that relay SR operates at the beginning of thestop pulse of a character signal transmitted to the line circuit, andtherefore the distortion caused by condenser Sc7 is bias rather than enddistortion.

When it is desired to send switched end distortion, a break signal issent from the outlying station to the line circuit usually at the timeswitched bias signals are being received yfrom the central oice. Underthese circumstances, the ground on the lower armature and back contactof relay SLS is connected over the inner lower armature and `frontcontact of relay 3ST, inner lower armature and front contact of relaySRY, to the stepping magnet ZSTPA which operates to step the brushes ofselector switch ZSWA from their respective contacts No. 6 to theirrespective contacts No. 7. When the brush on the rear contact bank ofselector switch ZSWA reaches contact No. 7 relay SED operates in a pathtraceable from Agrounded source SS-1 through resistor 3R12, ywinding ofrelay SED, conductor S32, contact No. 7 and brush of the rear contactbank of selector switch ZSWA, conductor S19, front contact and outerupper armature of relay SST, to ground. Rel-ay SED operates and uponoperating, closes a circuit at its right-hand armature and frontcontact, through the winding of relay SRY, resistor 3R11, to groundedsource SZS of positive potential of volts, and relay SRY, having startedto release when the brush of the rear contact bank of selector switchleaves contact No. 6, reoperates. Also relay SED, upon operating,transfers lat its left-hand armature, the condenser Sc7' from the outerlower armature of relay SR to the outer lower armature of relay SY. Whenrelay SY is not operated, condenser Sc7' is connected to the plate ofvacuum tube SB1 as it was before, and when relay SY is operatedcondenser S07 is connected to the plate of vacuum tube SBZ also asbefore. The dilference between the connection of condenser Sc7 to relaySY rather than to relay SR is that relay SY operates at the end of astop pulse of a character signal transmitted to the line circuit Whichmakes its eiect felt during the start pulse of the `following charactersignal. The switching of condenser S07' `from the plate of vacuum tubeSB1 to the plate of vacuum tube SBZ therefore occurs during the startpulse of a character signal, and end distortion rather than bias isproduced. The amount of end distortion should be the same -as the amountof bias that was produced since both are produced by the same values ofresistance in the plate circuits of vacuum tubes 'SB1 and SBZ and bythesamevalue of capacitance in condenser Sc7.

When it is desired to stop the transmission of R and Y signals subjectedto switched end distortion, the sending of a break signal from theoutlying station will cause selector switch SSWA to step its brushes totheir respective contacts No. 8. This will cause the release of relaySED which in turn will cause the release of relay SRY. The ground fromthe lower armature of relay SLS will therefore now be connected to thewinding of the release vmagnet ZRLSA in a path traceable from groundedsource 409 of negative potential of 24 volts, armature No. 2 and yfrontcontact of relay I4C, conductor Z510, through the winding of releasemagnet ZRLSA,

conductor 321, back contact and inner lower armature of relay 3RY,conductor 320, front contact and inner lower armature of relay 3ST, toground at the back contact and lower armature of relay SLS. Releasemagnet ZRLSA operates and restores stepping switch ZSWA to its normal,or zero, position to Stop the transmission of teletypewriter signals tothe line circuit.

It will be noted that with relays 3R, 3Y, SRY and BED released, which isthe normal condition, the condenser 3c7' is connected through theleft-hand armature and back contact of relay SED and the outer lowerarmature and back contact of relay 3R to the plate of tube 3B1. Asdescribed above, condenser 3c7, so connected, imposes spacing bias onsignals impressed on the grid of tube 3B1. Relay 3R and 3ED are releasedduring the transmission of the transmitter start signal patterns thatare selected for transmission under the control of relays 4R1 and SR1,and during the transmission of station connecting codes when any of therelays 4R2, 4K3, 4R4, SR2, 5R3 or 5R4 is operated. Thus those signalsare subjected to spacing bias and, as previously set forth, themagnitude of the spacing bias is of the order of 2O percent of a signalelement. The SOTUS units that receive the test signals are capable, whenin proper operating condition, of correctly interpreting receivedsignals having bias exceeding 20 percent. Accordingly, there should beno false selections when the SOTUS units are responding to signals sobiased, and any unit that fails to respond properly to the signals isfaulty and requires servicing. If it should be desired to eliminate thespacing bias except when the R and Y signals are transmitted, this maybe accomplished by having condenser 3c7 normally disconnected from theleft-hand armature of relay SED by suitable relay contacts.

Upon completion of the checking operation of the SOTUS unit at theoutlying station, the maintenance man thereat sends three break signalsto light calling-in lamp 612 at the testboard at the central oce. Theattendant will, upon observing the lighted lamp, connect telephoneheadset 61S to the line circuit for communicating with the maintenanceman. Upon receiving information to the effect that the checkingoperation at the outlying station is completed, the testboard attendantrestores the operated key 607, whereby the system at the central oice isrestored to normal.

What is claimed is:

1. In a telegraph system, a switching center, a station, a line circuitinterconnecting said switching center and said station, means at saidstation for transmitting a non-code control signal over said linecircuit, a telegraph signal responsive selector mechanism at saidstation, a source of telegraph signals at said switching center andmeans at said switching center responsive to one or more of said controlsignals incoming over said line circuit for selecting in accordance withthe number of control signals received, a desired group of telegraphsignals to be transmitted from said source for testing said selectormechanism.

2. In a telegraph system, a switching center, a station, a line circuitinterconnecting said switching center and said station, means at saidstation for sending a noncode control signal over said line circuit, atelegraph signal responsive selector mechanism at said Station, aplurality of sources of diiferent groups of telegraph signals at saidswitching center, means at said switching center responsive to a singletransmission of said control signal incoming over said line circuit forselecting a desired group of telegraph signals from one of said sourcesfor testing one of the selective characteristics of said selectormechanism, other means at said switching center responsive to additionaltransmissions of said control signal incoming over said line circuit forselecting another desired group of telegraph signals from another ofsaid sources to test another of the selective charaeteristics of saidselector mechanism, and still other 28 means at said switching centerresponsive to other additional transmissions of said control signalincoming over said line circuit for transmitting to said line circuittelegraph signals with various types of distortion.

3. In a telegraph system, a switching center, a station, a line circuitinterconnecting said switching center and said station, a manuallyoperable element at said station for transmitting break signals oversaid line circuit, a signal responsive selector mechanism at saidstation, sources of telegraph signals at said switching center, means atsaid switching center responsive to one or more break signals incomingover said line circuit for selecting in accordance with the number ofbreak signals received a desired group of telegraph signals from one oranother of said sources for accordingly testing the selectingcharacteristics of said selector mechanism, and other means responsiveto the operation of said break signal responsive means for causing saidbreak signal responsive means to be restored to its normal condition inresponse to an additional one or more break signals incoming over saidline circuit after a predetermined interval of time following theoperation of said break signal responsive means.

4. In a teletypewriter intercommunicating system, a switching center, aplurality of outlying stations, line circuits respectively connectingsaid outlying stations to said switching center, a teletypewriterreceiver at each of said stations, and means at each of said stationsfor transmitting break signals to said switching center, said switchingcenter comprising signal producing means, means responsive to said breaksignals for selecting a group of signals from said signal producingmeans, and signal transmitting means for automatically transmitting, inturn, from each of said selected groups to test the teletypewriterreceiver the outlying station in response to said break signals.

5. In a telegraph system, a switching center, a station, a line circuitinterconnecting said switching center and said station, means at saidstation for sending break signals over said line circuit, a telegraphreceiver at said station, a source of telegraph signals arranged toproduce signals in groups of various patterns, a testboard calling-insignal at said switching center, means at said switching centerresponsive (l) to a certain number of break signals incoming over saidline circuit for selecting the desired pattern of a plurality of groupsof signals from said source for etectively testing a particularcharacteristic of said receiver, (2) to another number of break signalsfor selecting the desired pattern for another plurality of a group ofsignals from said source for effectively testing another characteristicof said receiver, and (3) to still another number of break signals foroperating said calling-in signal to attract the attention of anattendant at said switching center.

6. In a telegraph system, a switching center, a plurality of stations,line circuits respectively connecting said stations to said switchingcenter, telegraph receivers at said stations, means at each of saidstations for transmitting break signals over the respective linecircuit, a source of telegraph signals at said switching center,rotatably operable means at said switching center responsive to onebreak signal incoming over any one of said line eircuits for selectingfrom said source a group of signals for testing a particularcharacteristic of said telegraph receivers, rotatably stepping meansarranged to operate one step in response to the transmission of each ofthe signals from said source during the time that the rotatably operablemeans is in its first operated position, Iand means for repeating thetransmission of said signals from said source as long as said rotatablyoperable means remains in its iirst operated position.

7. In a teletypewriter system, a switching center, a plurality ofstations, line circuits respectively connecting said stations to saidswitching center, means at each of said stations for transmitting break"signals over the rc- 29 's'pective line circuit, a teletypewriterreceiver connected to each of said line circuits, a source ofteletypewriter signals having switched bias, rotatably operable means atsaid switching center responsive to break signals incoming ovei any oneof said line circuits, automatically operating means including spacedischarge means controlled by said rotatably operable means in a certainone of its operated positions for transmitting to said line circuit aFigures signal and for automatically operating said rotatably operablemeans to its next operated position, other space discharge meanscooperating with said automatically operating means controlled by saidrotatably operable means in said next operated position for transmittingto said one line circuit a signal for the letter H and for automaticallyoperating said rotatably operable means to another of its operatedpositions, still other space discharge means cooperating with saidautomatically operating means and controlled by said rotatably operatedmeans in said other operated position for tras`- mitting signals of theletter R and Y alternately, delay circuit means cooperating With saidautomatically operating means and responsive during the production ofsaid alternate signals for impressing a marking bias of a predeterminedamount on each of the R signals and a spacing bias of the same amount oneach of the Y signals.

8. In a teletypewriter system according to claim 7 wherein saidrotatably operable means includes electromagnetic means responsive to anadditional break signal incoming over said line circuit and cooperatingwith said delay means for impressing marking end distortion of saidpredetermined amount on each of the R signals and spacing end distortionof the same amount on each of the Y signals.

No references cited.

